Add support for FileData (#92)

Per [b/330773378](https://b.corp.google.com/issues/330773378),

This adds support for the new `FileData` part type for referencing
storage files. This also adds "support" from the genai side, as a means
of catching future api discrepancies between common and genai.

.changes/crowd-birthday-drink-circle.json

@@ -0,0 +1 @@
+{"type":"PATCH","changes":["Implement error catching for unsupported Part types."]}

common/src/main/kotlin/com/google/ai/client/generativeai/common/shared/Types.kt

@@ -52,6 +52,14 @@ data class Content(@EncodeDefault val role: String? = "user", val parts: List<Pa
 
 @Serializable data class BlobPart(@SerialName("inline_data") val inlineData: Blob) : Part
 
+@Serializable data class FileDataPart(@SerialName("file_data") val fileData: FileData) : Part
+
+@Serializable
+data class FileData(
+  @SerialName("mime_type") val mimeType: String,
+  @SerialName("file_uri") val fileUri: String
+)
+
 @Serializable
 data class Blob(
   @SerialName("mime_type") val mimeType: String,
@@ -75,7 +83,8 @@ object PartSerializer : JsonContentPolymorphicSerializer<Part>(Part::class) {
     val jsonObject = element.jsonObject
     return when {
       "text" in jsonObject -> TextPart.serializer()
-      "inlineData" in jsonObject -> BlobPart.serializer()
+      "inline_data" in jsonObject -> BlobPart.serializer()
+      "file_data" in jsonObject -> FileDataPart.serializer()
       else -> throw SerializationException("Unknown Part type")
     }
   }

generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt

@@ -126,6 +126,10 @@ internal fun Part.toPublic(): com.google.ai.client.generativeai.type.Part {
         com.google.ai.client.generativeai.type.BlobPart(inlineData.mimeType, data)
       }
     }
+    else ->
+      throw SerializationException(
+        "Unsupported part type \"${javaClass.simpleName}\" provided. This model may not be supported by this SDK."
+      )
   }
 }